Chang Colón, Alejandra

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    Growth and sexual maturity determination in F1 Dorper x Criollo and Katahdin x Criollo males in a tropical climate
    (2023-05-12) Chang Colón, Alejandra; Fernández Van Cleve, John; College of Agricultural Sciences; Rodríguez Carías, Abner; Arcelay Ruíz, Enid; Latorre Acevedo, José R.; Department of Animal Science; Ortíz Bermúdez, Patricia
    Heat stress (HS) affects growth and reproductive efficiency in sheep. Climate change continues to increase ambient temperatures across the globe; therefore, sheep farmers must select rams tolerant to HS (temperature-humidity index > 82). The objective of this study was to compare and evaluate growth and sexual maturity in F1 crossbred rams raised under HS conditions. The study was carried out for a 15-month period at the small ruminant project of the University of Puerto Rico in Mayagüez. Eleven replacement rams were used, F1 Katahdin crosses with Criollo ewes (KxC, n=6), and F1 Dorper crosses with Criollo ewes (DxC, n=5). All 11 rams were born in November 2019 and weaned in February 2020. To evaluate growth rate during the pre-weaning period and for 52 weeks after weaning, weekly zoometric measurements (ZM), body weight (BW), and scrotal circumference (SC) were taken. At six months of age, semen collection began, and each ejaculate was measured for concentration (M/mL) and volume (mL). Statistical analysis of the data shows no significant differences when comparing ZM, BW, and SC between groups. However, compared to breed standards, KxC and DxC crosses reach a smaller size than purebreds. In both groups, the average semen volume was 1.51ml KxC cross and 1.13mL DxC cross throughout the experimental period with an average concentration of 1979.39 M/mL KxC cross and 1960.03 M/mL DxC cross. These values indicate that under HS, the crossbred rams reach sexual maturity at approximately 12.0 and 12.20 months of age, respectively. In conclusion, our results suggest HS affects growth and age at sexual maturity in crossbred rams from purebred dams and purebred sires by affecting feeding patterns. Therefore, the selection of males with greater adaptability to HS could be a valuable tool to improve the reproductive efficiency of our herds.